VALIDATION OF RAY ACOUSTICS APPLIED FOR THE MODELLING OF NOISE BARRIERS

Ray acoustics have been used to investigate the effectiveness of noise barriers in railway applications. Various types and shapes of barriers are modelled using the commercial software RAYNOISE. Absorbing and reflecting configurations as well as barriers at different angles are included. The numerical results are validated by measurement of the insertion loss for four types of barriers. A-weighted sound pressure levels have been calculated at six locations, 25 m from the track and are compared with the experimental values. The source strengths were selected to represent a high-speed train. The measurements were carried out using a microphone array; therefore the tests could be carried out alongside noise barriers of reduced length. The barrier measurements have already been validated against train pass-by measurements and have shown to be accurate within 1–2 dB (A). Insertion losses up to 15 dB (A) have been measured and calculated. Comparison between numerical and experimental values show agreement within 2 dB (A). The sensitivity of the numerical models to some numerical parameters as well as to the barrier-to-track distance was investigated. The results show that there is significant dependence on parameters, such as the number of rays and the order of reflection. Therefore, some guidelines are proposed in order to achieve stable results. In a single case of a reflecting barrier, the barrier-to-track spacing is quite critical, due to a reflection effect. The main conclusion is that ray acoustics can be a powerful tool in investigating the effectiveness of noise barriers, and that the accuracy of the calculated A-weighted sound pressure levels is within acceptable limits.